Catalytic Conversion of 1,3,5 TIPB Over Y-Zeolite based Catalysts Catalyst/oil ratio(C/O) Effect and a Kinetic Model
Abstract
A typical FCC unit involves the transport and rapid catalytic reaction of chemical species using 60-70 micron fluidizable catalyst particles. In FCC, hydrocarbon species evolve in the gas-phase are adsorbed on, and then react with the catalyst particles. In this case, large molecular weight hydrocarbons (vacuum gas oil) are converted into lighter products (gasoline). FCC also yields undesirable products such as light gases and coke. Coke promotes catalyst activity decay and as result, is detrimental to catalyst performance. Given the significance of coke as a catalyst decay agent in FCC, it is the objective of this PhD research to study catalyst deactivation by coke.
To accomplish this, three different Y-zeolite FCC catalysts, designated as CAT-A, CAT-B and CAT-C were employed in the present PhD study. Catalyst samples studied were characterized in terms of Crystallinity, Total Acidity, Specific Surface Area (SSA), Temperature Programmed Ammonia Desorption (NH3-TPD) and Pyridine Chemisorption.
Catalytic cracking runs were carried out in a CREC Riser Simulator using a model hydrocarbon species (1,3,5-TIPB) as a hydrocarbon feedstock. This bench-scale mini-fluidized batch unit mimics the operating conditions of large-scale FCC units. Temperatures within the 510°C-550°C range and times ranging from 3s-7s were selected for catalyst evaluation. For every experiment, 0.2g of 1,3,5-TIPB was contacted with a catalyst amount ranging from 0.12g to 1g. This was done to achieve a C/O ratio in the range of 0.6 to 5.
Results obtained showed a consistent 1,3,5-TIPB conversion pattern for the three catalysts studied: increasing first, stabilizing later, and finally decreasing modestly. In spite of this, coke formation and undesirable benzene selectivity always rose. On this basis, a mechanism involving both single catalyst sites for cracking and two sites for coke formation was considered. In this respect, coke formation was postulated as an additive process involving coke precursor species, which are either adsorbed on two sites located in the same catalyst particle or adsorbed in two close sites in different catalyst particles.